Current methodological approaches in conditioned pain modulation assessment in pediatrics

Pain-Related Stigma and Its Associations With Clinical and Experimental Pain Severity in Youth With Chronic Musculoskeletal Pain Conditions

OBJECTIVE

Many children with chronic musculoskeletal pain conditions experience stigma which can have negative downstream consequences. This study compares ratings of clinical pain (current pain intensity and pain interference), experimental pain (temporal summation, cold water tolerance, and cold pain intensity), and pain-related stigma among three groups of youth with rheumatic conditions. The relations among ratings of pain-related stigma and pain variables were explored.

METHODS

Eighty-eight youth aged 8-17 years with a diagnosis of juvenile idiopathic arthritis (JIA = 32), juvenile fibromyalgia (JFM = 31), or non-specific chronic pain (NSCP = 25) completed measures of clinical pain ratings (average 7-day pain intensity, day of assessment pain (DoA), and pain interference), experimental pain (cold pain tolerance, cold pain intensity, and temporal summation of mechanical pain), and pain-related stigma. Data analysis compared pain-related stigma and pain ratings across the three groups and examined the relations among pain-related stigma and pain ratings.

RESULTS

Youth with JFM reported higher ratings of clinical pain and pain-related stigma than their counterparts with NSCP or JIA. However, there were no differences in experimental pain. Pain-related stigma was associated with greater ratings of pain interference, particularly for those with JIA and NSCP. Pain-related stigma was also associated with greater average daily pain intensity but not DoA.

CONCLUSION

Youth with medically unexplained pain report greater stigma and worse pain than their peers; thus, robust assessment of pain in this population is necessary. Future work should longitudinally explore the impact of pain-related stigma on pain outcomes and treatment responses.

Clusters of facilitatory and inhibitory conditioned pain modulation responses in a large sample of children, adolescents, and young adults with chronic pain

Supplemental Digital Content is Available in the Text.

Findings from the current study add to the literature by describing different clinical phenotypes of central pain mechanisms of youth with chronic pain.

Introduction:

When investigating the role of facilitatory and inhibitory pain mechanisms such as conditioned pain modulation (CPM) and temporal summation of pain (TSP), it is important to take both into consideration in a single experimental model to provide the most information on subgroups of patients. Therefore, the objective of this study was to identify subgroups in a large population of pediatric patients with chronic pain based on their facilitatory and inhibitory pain mechanisms and compare them with control subjects.

Methods:

Five hundred twenty-one female subjects and 147 male subjects between 8 and 21 years old underwent a CPM assessment using a 2-minute tonic noxious heat stimulation as the test stimulus and a 2-minute cold-pressor task (CPT) (12°C) as the conditioning stimulus.

Results:

The best partition of clusters of patients was 3 clusters accounting for 27.15% of the total variation in the data. Cluster 1 (n = 271) was best characterized by high pain intensity during the CPT, lack of TSP during the test stimuli, and efficient inhibitory CPM. Cluster 2 (n = 186) was best characterized by low pain intensity during the CPT, lack of TSP during the test stimuli, and efficient inhibitory CPM. Cluster 3 (n = 151) was best characterized by high pain intensity during the CPT, presence of TSP during the test stimuli, and inefficient inhibitory CPM.

Discussion:

A single thermal CPM experimental design can identify combinations of facilitatory and inhibitory pain modulation responses. Findings from the current study add to the literature by describing different clinical phenotypes of central pain mechanisms of youth with chronic pain.

Conditioned Pain Modulation in Children: The Effects of Painful and Nonpainful Conditioning Stimuli

Conditioned pain modulation (CPM), a psychophysical measure in which 1 pain stimulus (conditioning stimulus) is used to inhibit another pain stimulus (test stimulus), is an important indicator of endogenous pain inhibition in adults, but is understudied in children. Preliminary evidence suggests that CPM effects are present in healthy children and are more robust in adolescents. However, developmental differences in younger children are not well documented and few studies control for potential distraction effects of the conditioning stimulus (CS). Participants were 54 healthy children aged 6 to 12 years. After a baseline pressure pain threshold (PPT) test, participants underwent 2 conditioning trials in which PPT was assessed while they placed their left hand in a water bath maintained at either 12 °C (painful CS) or 22 °C (nonpainful sham CS) in counterbalanced order. Results revealed a significant CPM effect. PPT values were significantly higher relative to baseline during the painful CS trial; PPT during the nonpainful CS trial did not differ from baseline. There were no significant age differences in magnitude of CPM effect. The results indicate that children as young as 6 years of age demonstrate CPM, suggesting that descending inhibitory pathways may be better developed in young children than previously thought. PERSPECTIVE: This study was successful in producing inhibitory CPM effects in physically healthy children while controlling for sensory distraction. The findings provide strong evidence that the obtained CPM responses cannot be attributed to sensory distraction or other nonspecific effects. Future studies could utilize CPM paradigms to study various aspects of pediatric endogenous pain inhibition, in order to better predict pain responses and improve interventions.

Phenotyping Chronic Musculoskeletal Pain in Male and Female Adolescents: Psychosocial Profiles, Somatosensory Profiles and Pain Modulatory Profiles

Purpose

A major limitation in treatment outcomes for chronic pain is the heterogeneity of the population. Therefore, a personalized approach to the assessment and treatment of children and adolescents with chronic pain conditions is needed. The objective of the study was to subgroup pediatric patients with chronic MSK pain that will be phenotypically different from each other based on their psychosocial profile, somatosensory function, and pain modulation.

Patients and Methods

This observational cohort study recruited 302 adolescents (10–18 years) with chronic musculoskeletal pain and 80 age-matched controls. After validated self-report questionnaires on psychosocial factors were completed, quantitative sensory tests (QST) and conditioned pain modulation (CPM) were performed.

Results

Three psychosocial subgroups were identified: adaptive pain (n=125), high pain dysfunctional (n=115), high somatic symptoms (n=62). Based on QST, four somatosensory profiles were observed: normal QST (n=155), thermal hyperalgesia (n=98), mechanical hyperalgesia (n=34) and sensory loss (n=15). Based on CPM and temporal summation of pain (TSP), four distinct groups were formed, dysfunctional central processing group (n=27) had suboptimal CPM and present TSP, dysfunctional inhibition group (n=136) had suboptimal CPM and absent TSP, facilitation group (n=18) had optimal CPM and present TSP, and functional central processing (n=112) had optimal CPM and absent TSP. A significant association between the psychosocial and somatosensory profiles. However, no association was observed between the psychosocial or somatosensory profiles and pain modulatory profiles.

Conclusion

Our results provide evidence that adolescents with chronic musculoskeletal pain are a heterogenous population comprising subgroups that may reflect distinct mechanisms and may benefit from different treatment approaches. The combination of screening self-reported questionnaires, QST, and CPM facilitate subgrouping of adolescents with chronic MSK pain in the clinical context and may ultimately contribute to personalized therapy.

Psychosocial and psychophysical assessment in pediatric patients and young adults with chronic back pain: a cluster analysis

Background

Identifying subgroups with different clinical profiles may inform tailored management and improve outcomes. The objective of this study was to identify psychosocial and psychophysical profiles of children and adolescents with chronic back pain.

Methods

One hundred and ninety‐eight patients with chronic back pain were recruited for the study. Pain assessment was mainly conducted in the form of an interview and with the use of validated pain‐related questionnaires assessing their psychosocial factors and disability. All patients underwent mechanical and thermal quantitative sensory tests assessing detection and pain thresholds, and conditioned pain modulation efficacy.

Results

Hierarchal clustering partitioned our patients into three clusters accounting for 34.73% of the total variation of the data. The adaptive cluster represented 45.5% of the patients and was characterized to display high thermal and pressure pain thresholds. The high somatic symptoms cluster, representing 19.2% of patients, was characterized to use more sensory, affective, evaluative and temporal descriptors of pain, more likely to report their pain as neuropathic of nature, report a more functional disability, report symptoms of anxiety and depression and report poor sleep quality. The pain‐sensitive cluster, representing 35.4% of the cohort, displayed deep tissue sensitivity and thermal hyperalgesia.

Conclusions

This study identified clinical profiles of children and adolescents experiencing chronic back pain based on specific psychophysical and psychosocial characteristics highlighting that chronic pain treatment should address underlying nociceptive and non‐nociceptive mechanisms.

Significance

To our current knowledge, this study is the first to conduct cluster analysis with youth experiencing chronic back pain and displays clinical profiles based on specific physical and psychosocial characteristics. This study highlights that in a clinical context, chronic pain assessment should include multiple elements contributing to pain which can be assessed in a clinical context and addressed when pathoanatomical symptoms are unidentifiable.

Health-related quality of life deviations from population norms in patients with lumbar radiculopathy: associations with pain, pain cognitions, and endogenous nociceptive modulation

PURPOSE

The primary goal of this study was to compare the health-related quality of life (HRQoL) of people with lumbar radiculopathy to age- and sex-adjusted population norms. Additionally, it aimed to explore the associations between the HRQoL difference scores and measures related to pain cognitions, pain intensity, and endogenous nociceptive modulation.

METHODS

Using answers from the Short Form 36-item Health Survey and UK population norms, SF-6D difference scores were calculated. A one-sample t test was used to assess the SF-6D difference scores. Univariate and multivariate regression analyses were used to assess the associations between SF-6D difference scores and pain intensity [Visual Analogue Scale (VAS) for back and leg pain], pain cognitions [Pain Catastrophizing Scale (PCS), Tampa Scale for Kinesiophobia (TSK), Pain Vigilance and Awareness Questionnaire (PVAQ)], and correlates for endogenous nociceptive modulation using quantitative sensory testing.

RESULTS

One hundred and twenty people with lumbar radiculopathy scheduled for surgery were included in this study. The mean SF-6D difference score of - 0.26 [SD = 0.09] was found to be significantly less than 0 [95%CI: - 0.27 to - 0.24]. Univariate analyses showed a significant influence from PCS, TSK, and PVAQ on the SF-6D difference scores. The final multivariate regression model included PCS and PVAQ, with only PCS maintaining a statistically significant regression coefficient [b = - 0.002; 95% CI: - 0.004 to - 0.001].

CONCLUSION

People diagnosed with lumbar radiculopathy report significantly lower HRQoL scores when compared with age- and sex-adjusted UK norm values. Even though all examined pain cognitions were found to have a significant association, pain catastrophizing showed the most significant relation to the SF-6D difference scores.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov Identifier No. NCT02630732. Date of registration: November 25, 2015.

Phenotyping peripheral neuropathic pain in male and female adolescents: pain descriptors, somatosensory profiles, conditioned pain modulation, and child-parent reported disability

ABSTRACT

Neuropathic pain (NeuP) can be difficult to diagnose and manage in children. Data regarding prevalence and sex-dependent differences are limited, and more detailed phenotyping is needed. This observational cohort study recruited adolescents (10-17 years) with NeuP or complex regional pain syndrome (CRPS). After pain history and NeuP questionnaires, quantitative sensory testing was performed. Individual z-score plots were calculated with body-region control measures and matched to mechanism-related sensory profiles (sensory loss, thermal hyperalgesia, and mechanical hyperalgesia). Conditioned pain modulation was assessed with pressure pain threshold and a contralateral cold conditioning stimulus, and meaningful conditioned pain modulation defined as twice the standard error of measurement. Patients and parents completed validated questionnaires for child quality of life (QoL), pain catastrophizing, and self-reported anxiety/depression. Males (n = 23) and females (n = 43) with NeuP (n = 52) or CRPS (n = 14) reported moderate-severe pain with neuropathic sensory descriptors. Mixed patterns of sensory gain/loss at pain sites were not sex-dependent. Thermal hyperalgesia was common in both NeuP and CRPS, whereas sensory loss occurred only with NeuP and in a smaller proportion than adult cohorts. Conditioned pain modulation was inhibitory in 54%, facilitatory in 14%, and nonresponders had variable cold conditioning sensitivity. Males and females reported marked impairment of QoL, increased emotional distress, and pain catastrophising. Child-parent QoL scores correlated, but catastrophizing scores were discordant when parents or adolescents reported higher anxiety/depression. NeuP in adolescents is associated with significant pain, physical impairment, and psychosocial impairment. Quantifying alterations in somatosensory profiles, descending modulation, child and parent psychological function will inform individualized therapy and stratification for future clinical trials.

Neuropathic pain in children: Steps towards improved recognition and management

Neuropathic pain in children can be severe and persistent, difficult to recognise and manage, and associated with significant pain-related disability. Recognition based on clinical history and sensory descriptors is challenging in young children, and screening tools require further validation at older ages. Confirmatory tests can identify the disease or lesion of the somatosensory nervous system resulting in neuropathic pain, but feasibility and interpretation may be influenced by age- and sex-dependent changes throughout development. Quantitative sensory testing identifies specific mechanism-related sensory profiles; brain imaging is a potential biomarker of alterations in central processing and modulation of both sensory and affective components of pain; and genetic analysis can reveal known and new causes of neuropathic pain. Alongside existing patient- and parent-reported outcome measures, somatosensory system research methodologies and validation of mechanism-based standardised end-points may inform individualised therapy and stratification for clinical trials that will improve evidence-based management of neuropathic pain in children.

Spatial aspects of pain modulation are not disrupted in adolescents with migraine

OBJECTIVE

To compare spatial pain modulation capabilities between adolescents with and without migraine.

BACKGROUND

Conditioned pain modulation (CPM) responses at the leg are similar in adolescents with versus without migraine. However, the anatomical region of testing may affect spatial pain modulation capabilities as differences in nociceptive processing between patients with migraine and healthy controls are found in local areas that are near the site of clinical pain but not in nonlocal areas. This study aimed to examine spatial pain modulation capabilities tested by the CPM paradigm using test stimulus applied to a local body area.

METHODS

Nineteen adolescents with migraine (age 14.9 ± 2.3, mean ± SD; 16 female) and 20 healthy adolescents (age 13.8 ± 2.5, mean ± SD; 16 female) completed this case-control study at Cincinnati Children's Hospital Medical Center. Pressure pain thresholds (PPT) were assessed at the trapezius before and during immersion of the foot in a cold water bath (8°C).

RESULTS

In the migraine group (146.0 ± 79.1, mean ± SD), compared to healthy controls (248.0 ± 145.5, mean ± SD), significantly lower PPT (kilopascal) values were found (estimate = 124.28, 95% CI: 58.98, 189.59, p < 0.001; effect size: d = 1.40). No differences between the groups were found for pain intensity and unpleasantness ratings of cold-water immersion nor the CPM response.

CONCLUSIONS

This study found altered ascending nociceptive processing of mechanical stimuli at the neck in adolescents with migraine. However, endogenous pain modulatory mechanisms were functional and not altered. In light of other studies, impairments in inhibitory control may not be involved in migraine pathophysiology in pediatric patients regardless of stimulus location.

Evidence of impaired pain modulation in adolescents with idiopathic scoliosis and chronic back pain

BACKGROUND CONTEXT

Although 40% of adolescent idiopathic scoliosis (AIS) patients present with chronic back pain, the pathophysiology and underlying pain mechanisms remain poorly understood. We hypothesized that development of chronic pain syndrome in AIS is associated with alterations in pain modulatory mechanisms.

PURPOSE

To identify the presence of sensitization in nociceptive pathways and to assess the efficacy of the diffuse noxious inhibitory control in patients with AIS presenting with chronic back pain.

STUDY DESIGN

Cross-sectional study.

PATIENT SAMPLE

Ninety-four patients diagnosed with AIS and chronic back pain.

OUTCOME MEASURES

Quantitative sensory testing (QST) assessed pain modulation and self-reported questionnaires were used to assess pain burden and health-related quality of life.

METHODS

Patients underwent a detailed pain assessment using a standard and validated quantitative sensory testing (QST) protocol. The measurements included mechanical detection thresholds (MDT), pain pressure threshold (PPT), heat pain threshold (HPT), heat tolerance threshold (HTT), and a conditioned pain modulation (CPM) paradigm. Altogether, these tests measured changes in regulation of the neurophysiology underlying the nociceptive processes based on the patient's pain perception. Funding was provided by The Louise and Alan Edwards Foundation and The Shriners Hospitals for Children.

RESULTS

Efficient pain inhibitory response was observed in 51.1% of patients, while 21.3% and 27.7% had sub-optimal and inefficient CPM, respectively. Temporal summation of pain was observed in 11.7% of patients. Significant correlations were observed between deformity severity and pain pressure thresholds (p=.023) and CPM (p=.017), neuropathic pain scores and pain pressure thresholds (p=.015) and temporal summation of pain (p=.047), and heat temperature threshold and pain intensity (p=.048).

CONCLUSIONS

Chronic back pain has an impact in the quality of life of adolescents with idiopathic scoliosis. We demonstrated a high prevalence of impaired pain modulation in this group. The association between deformity severity and somatosensory dysfunction may suggest that spinal deformity can be a trigger for abnormal neuroplastic changes in this population contributing to chronic pain syndrome.

Can disbudding of calves (one versus four weeks of age) induce chronic pain?

BACKGROUND

Calf disbudding is a welfare-relevant invasive husbandry procedure. While it is widely recognized that disbudding elicits acute pain, its chronic consequences are currently unknown.

OBJECTIVES

Primary aim of this study was to investigate whether disbudding leads to chronic pain in calves; secondary aim was to evaluate the influence of age at disbudding (1 week versus 4 weeks).

METHODS

Thirty-four Holstein bull calves, enrolled in a prospective, controlled, randomized trial, underwent either early disbudding (ED) or late disbudding (LD) or sham treatment (control) at 1 and 4 weeks of age. Pain scoring and quantitative sensory tests (von Frey filaments and algometry) were performed at regular intervals up to 105 days of life; neurophysiological determination of nociceptive reflex thresholds and conditioned pain modulation (CPM) up to 90 days. Data was analyzed with the Brunner and Langer model followed by post-hoc test, with level of significance set at 0.05.

RESULTS

Thirty-one calves completed the data collection. Signs of chronic sensitization were observed in 38% of disbudded calves (4 in ED and 4 in LD). Pain scores (until 105 days) and allodynia scores (until 60 days) were significantly higher while pressure thresholds (until 105 days) were significantly lower in both groups ED and LD compared to control. Late disbudded calves showed impairment of trigeminal CPM. Lower laser-evoked trigeminal reflex thresholds were found in clinically painful calves compared to control.

CONCLUSIONS

The sequelae of disbudding can extend beyond the acute post-procedural phase. Chronic trigeminal sensitization, independently from the age at disbudding can affect individual calves.